Optical system for intruder detecting device

ABSTRACT

An optical system for an intruder detector which employs an infrared ray detecting element and a parabolic mirror above the infrared detecting element for collecting infrared rays from a detection region and directing them onto the infrared ray detecting element, and which has a detecting range through a wide visual field of 360°. Reflecting mirrors 3 having the visual field of 360° are disposed around the outside of a parabolic mirror and confront the parabolic mirror 1 around the outer periphery of the infrared ray detecting element 2. A window 5 which transmits infrared rays and does not shield the visual field of the mirror 3 mounts the parabolic mirror 1 at a prescribed position with respect to a base 6. A convex lens 15 located at the conical axis of the parabolic mirror 1 forms another detection region directly under the intruder detecting device. The intruder detector using this optical system is mainly for mounting on the ceiling of a house.

TECHNICAL FIELD

This invention relates to an optical system of a device for detectingintruders which makes use of a straight beam of light or infrared rays.

BACKGROUND ART

Presently known intruder detectors making use of a straight beam oflight or infrared rays generally utilize a parabolic mirror as anoptical element to increase the density of a collected beam in aprojecting or an accepting direction, the focal position of the mirrorbeing occupied by a photo-electric transducer.

A passive type intruder detector compares infrared energy radiated froman intruder's body with infrared energy radiated from a backgroundmaterial object and generates an output signal when there is adifference above a predetermined level. An intruder detecting device ofthis type is disclosed in Japanese Laid-Open Utility Model PublicationNo. 97,534 of 1980 and Japanese Laid-Open Patent Publication No. 143,694of 1980. Because the visual field of this infrared detector is a maximumangle of 90 degress, any extension of a detecting region beyond saidvisual field is dependent upon the optical elements in the system. Inthe device disclosed by said Laid-Open Patent Publication No. 143,694 of1980, the sensing region may be extended to an angle of approximately180 degrees by combining a parabolic mirror with an alignment structureof plane mirrors. However, where the device is mounted on the ceiling ofa structure, the device has no sensitivity in the backward direction orgenerally in the downward direction. It should also be noted that thealignment structure of the plane mirrors is arranged into steps ofmirrors, and therefore, it is different to incline each of the dividedplane mirrors with respect to the optical axis of the parabolic mirrorso as to obtain a larger number of directions sensitive to intruders,and to equalize all the effective projecting areas of the dividedmirrors onto the parabolic mirror. Another difficult problem in theprior device is that each of the outer distributed plane mirrors cannotproject their whole mirror surface onto the parabolic mirror, andtherefore a substantial difference exists between the sensitivity of theinner and the outer mirrors.

It is an object of the invention to solve the above technical problemsby providing a simply constructed optical system for an intruderdetector in which the detecting region expands an angle of 360 degrees,and in which no substantial difference in sensitivity is present for thevarious detecting directions.

DISCLOSURE OF THE INVENTION

To achieve the above object of the invention, an infrared ray detectingelement is disposed at the focal position of a parabolic mirror. Facingthe parabolic mirror is a conical reflecting mirror which is disposed insuch a manner that it surrounds the infrared detecting element so thatits visual field covers the periphery of the parabolic mirror. Thereflecting mirror is comprised of a plurality of divided mirrorelements. Each of the mirror elements is directed to a particulardetecting region so that all the mirror elements together cover adetecting field having an angle of 360 degrees around the infrareddetecting element. If the angle of inclination of each mirror elementwith respect to the optical axis of the parabolic mirror is modified,the angular extent of the detecting field may be varied. Perforatedthrough the central portion of the parabolic mirror, perpendicular toits optical axis, is an opening having an inner diameter substantiallythe same as the outer diameter of the infrared detecting element. Aconvex lens mounted in the opening is focused on the activation surfaceof the infrared detecting element. The parabolic mirror is mounted to abase member through a cylindrical window member which is transparent toinfrared rays. An optical masking plate is provided with a plurality ofslits each corresponding to one of the gaps between adjacent dividedmirrors. The masking plate is disposed in a fixed position between theparabolic mirror and the reflecting mirror to allow the slit portions tomake the projections of detection.

The reflecting mirror can easily be molded, since the form of the mirroris a simple one such as a cone. Optical sensitivity in each of theindividual detection directions can be made uniform by the conical form,even though a significant directional detection in each of the detectiondirections is made to increase the density of collection of infraredrays. The window, which has a good transparency to infrared rays, allowsthe parabolic mirror to be correctly positioned with respect to the basemember without any post supporting the parabolic mirror.

This allows the detection regions covered by the device to extend overan angular extent of 360 degrees. The portion of the parabolic mirrorsurrounding its optical axis cannot effectively direct a beam reflectedfrom the reflecting mirror to the infrared detecting element. However, aconvex lens fitted in said portion allows an intruder immediately belowthe device to be detected. The extent of the detection region relativeto the optical axis of the parabolic mirror is controlled by theselection of the angle of inclination with respect to the optical axis.The masking plate eliminates from the detection field any backgroundthat may cause a false alarm due to unstable infrared energy radiationtherefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the exterior of an intruder detecting deviceaccording to the invention;

FIG. 2 is a partial cross sectional view of the device shown in FIG. 1;

FIG. 3 is a plan view of an optical masking plate;

FIG. 4 is a cross sectional view partially cut away of the deviceshowing the arrangement of a visual light source at the portion aboutthe focal point of a parabolic mirror; and

FIG. 5 is a plan view of the region detected by a reflecting mirrorconsisting of a plurality of divided plane mirrors.

BEST MODE OF CARRYING OUT THE INVENTION

The preferred embodiment of the invention will now be described inconjunction with the reference numerals shown in the drawings.

An infrared ray detecting element (hereinafter "detecting element") 2and a wiring substrate 9 are both placed within a base member 6. Thesubstrate 9 supports an electric circuit (not shown) which produces anoutput when any intruder is approaching the device. The base member 6 isalso provided with a conical reflecting mirror 3 surrounding thepheriphery of the detecting element 2. The mirror 3 is comprised of twogroups of mirrors 3a and 3b each having inclination angles with respectto the optical axis of a parabolic mirror 1 (as later described)different from each other. The groups of mirrors 3a and 3b are alsocomprised of a plurality of divided plane mirrors 3am and 3bn,respectively. All the divided mirrors in the two groups are made to havedirectivities along the individual detecting directions to increaselight collecting density. THe boundary between every adjacent two innerdivided mirrors 3am is circularly displaced from the boundary betweenevery adjacent two outer divided mirrors 3bn. Thereby, a blank detectionarea in each of the boundaries can be compensated for with thecorresponding divided mirror 3am to form a detecting field radiallyextending 360 degrees. A masking plate 4 is interposed between thereflecting mirror 3 and the parabolic mirror 1, and a through-holed boss11 of the plate is fitted in a bore of the center portion of thereflecting mirror 3. The masking plate 4 includes a plurality ofradially extending slits 14 wich divide the plate into a plurality ofinner and outer segment portions 13a and 13b, respectively, whileleaving inner and outer yoke sections 12a and 12b. The segment portions13a and 13b are separate from the yoke sections. The plurality ofsegment portions 13a correspond to the divided plane mirrors 3am, whilethe other plurality of segment portions 13b correspond to the otherdivided plane mirrors 3bn. Travelling through the slits or cut-offportions 14 between the segment portions 13a and 13b are infrared raysfrom the detecting field which are incident upon the parabolic mirror 1and infrared rays which are reflected from mirror 1 and directed to thedetecting element 2.

The parabolic mirror 1 is mounted to the base member 6 by a cover-likewindow 5 which is transparent to infrared rays. The focal point of theparabolic mirror 1 is caused to correspond with the activation surfaceof the detecting element 2 by the location thereof. At the centralportion about the optical axis of the parabolic mirror 1 a central boreis provided to fit therein a convex lens 15. The focal point of theconvex lens 15 is caused to correspond with the activation surface ofthe detecting element 2 so that a detecting field along the optical axisof the parabolic mirror can also be established.

The infrared ray transparent window 5 is detachable from the base member6 by releasing a fitting holding the window on the member. Therefore,the visual recognition of detecting regions by the detecting element 2can be achieved. The operation of said visual recognition is comprisedof the steps of placing a visual light source 7 such as a photo-diodewhich had been independently prepared, near the focal point of theparabolic mirror 1 using a support member 8; applying to said lightsource 7 a voltage from an electric supply pin member 10 provided on thewiring substrate 9; and visually observing the lighting field from saidenergized light source 7. In this case, a pedestrian check and anassociative indication cannot be executed to dynamically recognize thedetecting field.

FIG. 5 is a plan view showing the detection regions 3a' covered by theinner divided plane mirrors 3am and the detection regions 3b' covered bythe outer divided plane mirrors 3bn. The amount of infrared rays whichare collected by such mirrors can be increased by limiting the width ofeach of the detection regions 3a' and 3b'. This allows the electric gainof the device to be correspondingly decreased so as to eliminate anyoutcoming noise, and in particular, errors caused by electric wavedisturbances. The divided plane mirrors may also be replaced with anyrounded mirrors. In this case, the extent of cross sectional areaperpendicular to each detection direction will be varied.

I claim:
 1. An optical system for an intruder detector device includinga parabolic mirror and an infrared detecting element positioned at thefocal point of said parabolic mirror for detecting the entry of anintruder and generating an output signal in response to said entry,comprising:a conical reflecting mirror positioned at the periphery ofsaid infrared detecting element and facing the parabolic surface of saidparabolic mirror, the visual field of said reflecting mirror coveringsaid parabolic mirror up to its periphery, said reflecting mirror beingan assembly comprised of a plurality of divided plane mirrors separatedinto an inner group and an outer group circularly displaced from saidinner group; and a convex lens disposed at the center of the parabolicmirror, and being perpendicular to the optical axis thereof, said lenshaving substantially the same diameter as the outer diameter of thedetecting element, and focussing infrared rays from immediately belowthe detector device onto the activation surface of the detectingelement.
 2. An optical system for an intruder detector device as recitedin claim 1 wherein said divided plane mirrors of said reflecting mirrorhave a predetermined plurality of angles relative to the optical axis ofthe parabolic mirror.
 3. An optical system for an intruder detectordevice as recited in claim 1 wherein said parabolic mirror is mounted onand supported by an infrared transparent window so that the detectionregion covered by said detector is extended in all directions, saidwindow being attached to a base member mounting said detecting elementand acting as a cover for said parabolic mirror.